Copending application, Ser. No. 559,421 discloses production of bicomponent polyester fibers in a side-by-side arrangement wherein the two polymeric components are polyethylene terephthalate and sparingly cross-linked polybutylene terephthalate. Conventional processes for obtaining the bicomponent fibers are utilized. The filaments of this copending application exhibit good crimp properties, when compared to the bicomponent polyester filaments produced previously, but the crimp properties are still not as high as desired, principally when the sparingly cross-linked polybutylene terephthalate used has a molten state viscosity VF between 3500-5500 poises at 260.degree. C.
U.S. Pat. No. 3,671,379 to Evans, et al discloses the production of laterally eccentric bicomponent filaments, wherein one of the polymeric components can be polytetramethylene terephthalate and the other polymeric component can be polyethylene terephthalate. Such yarns are helically crimpable, and the crimp potential is retained when the filament is annealed. The two melts flow through individual channels to the front fact of the spinneret, wherein they merge into a side-by-side composite filament as they leave the spinneret assembly.
British Pat. No. 514,638 discloses a process for producing bicomponent filaments wherein the filaments are spun through a spinning nozzle which comprises two parallel plates having multiple perforations therein. One plate forms the outer wall of the nozzle and the other plate, which is separated a relatively small distance apart from the first plate, divides the interior of the nozzle into two separate compartments. Each plate contains the same number of perforations, and the opposed perforations are coaxial with each other. The two liquids to be spun are supplied to separate compartments, with the first liquid extruded through the inner plate in the form of liquid streams or jets into the compartment filled with the second liquid, which is in turn extruded through the outer plate into a precipitating medium in such a manner that it drags with it the streams of the first liquid. The apparatus can be used to produce concentric layers of the spun substances, or by using baths having a powerful shrinking action, fibers of various cross-sections can be obtained, and the inner polymer may lie on the surface of the fibers.
The aforesaid British Pat. No. 514,638 corresponds to French Pat. No. 837,555. French Pat. No. 50,780 is a third patent of addition to the aforesaid French Pat. No. 837,555. That patent of addition discloses that the distance between the two plates in the spinning nozzle can be varied to vary the configuration of the resulting filament. Furthermore, the opposed perforations can be displaced either radially or laterally, to also vary the characteristics of the resulting filaments. The working examples of this patent of addition relate to the first embodiment mentioned above, wherein the distance between the plates is varied to vary the filament properties, and no example discloses the radial or lateral displacement of the opposed perforations. That is, in the working examples of this third patent of addition, the opposed perforations are still substantially coaxial.